Plants 'mess up' climate change predictions

Thursday, 30 August 2007 Michael KahnReuters

Increased carbon dioxide levels with climate change will make it harder for plants to draw up water from the soil and out through their leaves, scientists say. So soils will become waterlogged, leading to more flooding than predicted (Image: iStockphoto)

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Current predictions for global warming underestimate the risk of floods and overestimate the impact of droughts by not taking into account the role plants play in absorbing carbon dioxide, researchers say.

They found higher levels of the greenhouse gas predicted for the end of the century will lead to an increase in the amount of water that plants hold in the soil, says Dr Richard Betts, a meteorologist at the UK's Met Office who led the study.

This means areas expected to see increased rainfall might have more severe flooding while droughts in other regions may not be as bad, he says.

"People may be underestimating flood risks because they do not expect the soil to be as saturated as it might be," Betts says.

"We also suggest the conservation of water by plants would partly offset the scarcity during a drought."

The findings, published today in the journal Nature, underscore the need to take a wider view of climate change to better understand and predict the impact of rising temperatures, he adds.

Using global climate models linked to data on vegetation and soil content, the team of UK researchers measured the effect of carbon dioxide levels expected to rise dramatically by the end of the century.

During photosynthesis carbon dioxide enters plants through tiny pores called stomata. Water eventually evaporates back into the atmosphere through these stomata.

But higher levels of carbon dioxide in the air cause these tiny holes to not open as widely, leading to reduced water loss from the plant and leaving more water in the soil, Betts says.

"Climate change is more than just a change in the meteorological conditions. It is also a change in the whole ecology," he says.

"We need to study this to get the whole picture because this hasn't been looked at before."

More flooding

With plants extracting less water from the soil, the surplus water will drain into rivers and increase global flows another 6% on top of the 11% rise already predicted due to global warming, Betts says.

The study does not indicate which areas might experience the greatest change but Betts says this is the next step for his team.

"We will need to quantify things and look at things like water availability and the details of how intense rainfalls may turn into flash floods," he says.